Hmmm... I guess where to start is first I've been in your position quite recently actually. But from an avid gamer to another avid gamer let me give you two really good tips to get you started.

1. First write down your idea, document it so specifically that you know exactly how you want the game to run on every level. From client side to server side. Know your game first, its no good to you if you just have an idea. You need to write a game design document. This will help you focus yourself and also people in game programming and development are more likely to help you.

2. Find a language that you like and can understand with game and network libraries. Or you can at least understand enough of the technology behind a web-based game to be able to talk to a programmer technically. For example, most browser based games are written in Flash with a lot of ActionScripting. Do you know enough about Flash or ActionScripting or programming concepts just to have a decent conversation with a programmer about how to translate your Design Document into a Flash game?

Once you have these things then you can actually get started with the design and implementation of your game. I hope this helps.